Two-stroke internal combustion engine with improved air intake system

ABSTRACT

A two-stroke internal combustion engine comprising an engine block, a plurality of crankcases and including a mounting surface having therein a plurality of inlet openings each communicating with a respective one of the crankcases, a throttle housing defining a throttle passage and including a plenum mounting surface, a throttle valve in the throttle passage, and a plenum member which is separable from both the engine block and the throttle housing and which defines a plurality of intake passages each having an outlet end communicating with a respective one of the inlet openings and each having an inlet end communicating with the throttle passage such that the intake of the engine can be tuned solely by modifying the configuration of the plenum member.

RELATED APPLICATION

This is a continuation-in-part of U.S. Ser. No. 07/954,492, filed Sep.30, 1992, now U.S. Pat. No. 5,273,016 (Atty. Docket No. 72012/1040).

BACKGROUND OF THE INVENTION

The invention relates to internal combustion engines, and moreparticularly to intake systems for two-stroke engines. Still moreparticularly, the invention relates to air intake systems for two-strokeengines in which fuel is injected directly into the cylinders.

SUMMARY OF THE INVENTION

The invention provides a two-stroke internal combustion enginecomprising a cylinder block including a generally planar crankcasemounting surface having therein a crankcase recess, a crankcase coverincluding a generally planar cylinder block mounting surface mating withthe crankcase mounting surface and having therein a crankcase recessaligned with the crankcase recess in the cylinder block and definingtherewith a crankcase, and air intake means for supplying a flow of airto the crankcase, the air intake means defining a U-shaped air intakepath having a downstream leg directed toward and generally perpendicularto the crankcase mounting surface and having an upstream leg generallyparallel to and directed opposite the downstream leg.

The invention also provides a two-stroke internal combustion enginecomprising engine block means defining a crankcase and including anintake manifold mounting surface having therein an inlet openingcommunicating with the crankcase, an intake manifold having a crankcasecover mounting surface mating with the intake manifold mounting surface,a plenum mounting surface opposed to the crankcase cover mountingsurface, and an intake passage extending from the plenum mountingsurface to the crankcase cover mounting surface, and a plenum coverincluding an inner surface mating with the plenum mounting surface, theplenum cover cooperating with the intake manifold to define, between theplenum cover and the intake manifold, an intake runner passagecommunicating with the intake passage and extending laterally from theintake passage.

The invention also provides a two-stroke internal combustion enginecomprising a cylinder block including a generally planar crankcasemounting surface having therein a crankcase recess, a crankcase coverincluding a generally planar cylinder block mounting surface mating withthe crankcase mounting surface and having therein a crankcase recessaligned with the crankcase recess in the cylinder block to define acrankcase, air intake means for supplying air to the crankcase, theintake means including a wall partially defining an air passagewaycommunicating with the crankcase, the wall having therein an openingcommunicating with the passageway, and an electronic control unitmounted on the wall and overlying the opening.

The invention also provides a two-stroke internal combustion enginecomprising an engine block means defining a crankcase and including anintake manifold mounting surface having therein an inlet openingcommunicating with the crankcase, an intake manifold including acrankcase cover mounting surface mating with the intake manifoldmounting surface, a plenum mounting surface opposed to the crankcasecover mounting surface, an intake passage extending from the plenummounting surface to the crankcase cover mounting surface andcommunicating with the inlet opening, and a throttle passage extendingfrom the plenum mounting surface and parallel to the intake passage, thethrottle passage being laterally offset from the intake manifoldmounting surface, and means for conducting air from the throttle passageto the intake passage.

The invention also provides an outboard motor having forward andrearward ends and comprising a propulsion unit adapted to be mounted onthe transom of a boat, the propulsion unit including a propeller shaftwith a rearward end adapted to have mounted thereon a propeller, and thepropulsion unit also including a two-stroke internal combustion enginedrivingly connected to the propeller shaft, the engine including engineblock means defining a crankcase and air intake means for supplying airto the crankcase, the air intake means defining a U-shaped air intakepath having a rearwardly directed downstream leg and having a forwardlydirected upstream leg generally parallel to the downstream leg.

The invention also provides a two-stroke internal combustion enginecomprising engine block means defining a plurality of crankcases andincluding a mounting surface having therein a plurality of inletopenings each communicating with a respective one of the crankcases, athrottle housing defining a throttle passage and including a plenummounting surface, a throttle valve in the throttle passage, and a plenummember which is separable from both the engine block means and thethrottle housing and which defines a plurality of intake passages eachhaving an outlet end communicating with a respective one of the inletopenings and each having an inlet end communicating with the throttlepassage such that the intake of the engine can be tuned solely bymodifying the configuration of the plenum member.

One of the features of the invention is the provision of an outboardmotor including a two-stroke engine having relatively few parts. Thissimplifies the manufacture and assembly of the engine. The engine alsohas a tuned air intake and is configured to fit within existing outboardmotor cowlings.

Another feature of the invention is the provision of a two-stroke enginehaving an air intake that can be tuned for optimum performance over arange of engine speeds. The range of engine speeds for which the engineis tuned can be easily changed by modifying the configuration of asingle engine component.

Another feature of the invention is the provision of a two-stroke enginehaving an air intake and an electronic control unit that is supported bythe air intake. The electronic control unit is cooled by air flowingthrough the air intake. The provision of an air-cooled electroniccontrol unit eliminates the need for a water jacket for cooling theelectronic control unit.

Other features and advantages of the invention will become apparent tothose skilled in the art upon review of the following detaileddescription, claims and drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side elevational view of an outboard motor embodyingthe invention.

FIG. 2 is a top view of the engine that is illustrated by FIG. 1 andthat is a first alternative embodiment of the invention.

FIG. 3 is an enlarged right side elevational view of a portion of theengine shown in FIG. 1.

FIG. 4 is a cross-sectional view taken along line 4--4 in FIG. 3.

FIG. 5 is an exploded top view of the engine shown in FIG. 2.

FIG. 6 is a cross-sectional view taken along line 6--6 in FIG. 2.

FIG. 7 is a partial cross-sectional view of the engine taken along line7--7 in FIG. 4.

FIG. 8 is a view taken along line 8--8 in FIG. 5.

FIG. 9 is a view taken along line 9=9 in FIG. 5.

FIG. 10 is a view taken along line 10--10 in FIG. 5.

FIG. 11 is a view taken along line 11--11 in FIG. 5.

FIG. 12 is a view taken along line 12--12 in FIG. 5.

FIG. 13 is a view taken along line 13--13 in FIG. 5.

FIG. 14 is an exploded, perspective view of a portion of the engineshown in FIG. 2.

FIG. 15 is a view similar to FIG. 2 illustrating an engine that is analternative embodiment of the invention.

FIG. 16 is a view similar to FIG. 3 illustrating the engine shown inFIG. 15.

FIG. 17 is a view similar to FIG. 8 illustrating a portion of the engineshown in FIG. 15.

Before one embodiment of the invention is explained in detail, it is tobe understood that the invention is not limited in its application tothe details of the construction and the arrangements of components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An outboard motor 10 that is a first embodiment of the invention isillustrated in FIGS. 1-14. As shown in FIG. 1, the outboard motor 10includes a propulsion unit 14 mounted on the transom 16 of a boat 18 forpivotal movement relative thereto about a generally horizontal tilt axis22 and about a generally vertical steering axis 26. The propulsion unit14 includes a propeller shaft 30 having a rearward end 34 having mountedthereon a propeller 38, and an internal combustion engine 42 drivinglyconnected to the propeller shaft 30 via a conventional drive train 46.

The internal combustion engine 42 is preferably a two-stroke, V-6engine. The engine 42 comprises (FIGS. 2 and 5) a V-type cylinder block50 having forward and rearward ends 54, 58. The rearward end 58 includesfirst and second or port and starboard cylinder banks 62, 66 havingrespective port and starboard cylinder head mounting surfaces 70, 74.Each cylinder bank 62, 66 includes (FIG. 4) three vertically alignedcylinders 78 (only one of which is shown). The forward end 54 of thecylinder block 50 defines (FIGS. 5 and 12) a forwardly facing, generallyplanar crankcase mounting surface 82 having therein (FIG. 12) sixcrankcase recesses 86. Each of the crankcase recesses 86 communicateswith a respective one of the cylinders 78 via (FIG. 4) one or moretransfer passages 90, as is known in the art. Such a cylinder blockconstruction is conventional and will not be described in greaterdetail.

The engine 42 also comprises six pistons 94 (only one shown in FIG. 4)slidably housed in respective cylinders 78, three of the pistons 94being housed by cylinders 78 in the starboard cylinder bank 66 and threepistons 94 being housed in the port cylinder bank 62.

The engine 42 also comprises (FIGS. 2 and 5) first and second or portand starboard cylinder heads 98, 102 respectively mounted on the portand starboard cylinder head mounting surfaces 70, 74 of the cylinderblock 50. The starboard cylinder head 102 closes the three starboardcylinders 78 and thus cooperates with the cylinder block 50 and with thepistons 94 housed in the starboard cylinders 78 to define (FIG. 4) threecombustion chambers 106 (only one shown). Similarly, though not shown inthe drawings, the port cylinder head 98 closes the port cylinders 78 andthus cooperates with the cylinder block 50 and with the pistons 94housed in the port cylinders 78 to define three combustion chambers 106.Each combustion chamber 106 communicates with a respective one of thecrankcase recesses 86 in the forward end 54 of the cylinder block 50 viaa respective one of the transfer passages 90.

The engine 42 also comprises (FIGS. 2 and 5) means 110 for injectingfuel directly into each of the combustion chambers 106 during engineoperation. While various suitable direct fuel injecting means 110 can beemployed, in the illustrated embodiment, the engine 42 includes threefuel injectors 114 which are supported by the port cylinder head 98 (oneshown in FIGS. 2 and 5), and three fuel injectors 114 which aresupported by the starboard cylinder head 102 (one shown in FIGS. 2 and5). Each fuel injector 114 is operable for injecting fuel directly intoa respective one of the combustion chambers 106 (shown in FIG. 4).Suitable means (not shown) are provided for supplying fuel underpressure to the fuel injectors 114.

The engine 42 also comprises (FIGS. 2, 5, 6, 10 and 13) a crankcasecover 118 mounted on the forward end 54 of the cylinder block 50. Thecrankcase cover 118 includes (FIGS. 4, 5 and 13) a rearwardly facing,generally planar cylinder block mounting surface 122 mating with thecrankcase mounting surface 82 so that the cylinder block mountingsurface 122 and the crankcase mounting surface 82 lie in a substantiallyvertical plane. The cylinder block mounting surface 122 has therein(FIGS. 6 and 13) six rearwardly opening crankcase recesses 126. Each ofthe crankcase recesses 126 aligns with a respective one of the crankcaserecesses 86 in the cylinder block 50 to define therewith a crankcase 130(FIGS. 4 and 6).

The crankcase cover 118 also includes (FIGS. 5, 6 and 10) a generallyplanar intake manifold mounting surface 134 facing forwardly or oppositethe cylinder block mounting surface 122. The intake manifold mountingsurface 134 has therein (see FIG. 10) six vertically aligned crankcaseinlet openings 138. In other words, all of the inlet openings 138 arein-line, i.e., are centered on a single vertical line 140 (FIG. 10). Asshown in FIG. 6, each of the crankcase inlet openings 138 communicateswith a respective crankcase 130 by means of a crankcase cover passageportion 142 extending between the crankcase inlet opening 138 and arespective crankcase recess 126 in the crankcase cover 118. Any suitablemeans (not shown) can be employed for securing the crankcase cover 118to the cylinder block 50.

The engine 42 also comprises (FIGS. 4 and 6) a crankshaft 150 supportedby the cylinder block 50 and the crankcase cover 118 for rotation abouta vertical axis lying the in the plane defined by the crankcase mountingsurface 82 and cylinder block mounting surface 122. As is known in theart, the crankshaft 150 includes (see FIG. 6) disc-like portions 154separating the adjacent crankcases 130. As is known in the art, thecrankshaft 150 is connected to each of the pistons 94 by a respectivepiston rod 162 (one shown in FIG. 4).

It should be understood that the cylinder block 50 and the crankcasecover 118 can be considered to be a single engine block means supportingthe crankshaft 150 and defining the crankcases 130.

The engine 42 also comprises air intake means 170 for supplying air toeach of the crankcases 130. While various suitable constructions for theair intake means 170 can be used, in the illustrated embodiment, the airintake means 170 defines (see FIG. 4) a U-shaped air intake path 174having a downstream leg 178 directed rearwardly or toward and generallyperpendicular to the crankcase mounting surface 82 and an upstream leg182 extending generally parallel to and directed forwardly or oppositethe downstream leg 178.

More particularly, and as shown in FIGS. 4, 5, 8 and 11, the air intakemeans 170 includes an intake manifold 190 mounted on the forward end ofthe crankcase cover 118. The intake manifold 190 includes integrallycast port and starboard portions 194, 198. The port and starboardportions 194, 198 both include (FIG. 8) a forwardly facing, generallyplanar plenum mounting surface 202. The plenum mounting surface 202 hastherein a series of six in-line, vertically aligned intake manifoldinlets 206 located in the forward face of the port portion 194.

The port portion 194 also includes (FIGS. 5 and 11) a rearwardly facing,generally planar crankcase cover mounting surface 210 that mates withthe intake manifold mounting surface 134. The crankcase cover mountingsurface 210 extends generally parallel to the plenum mounting surface202 and has therein a series of six in-line, vertically aligned intakemanifold outlets 214. As shown in FIGS. 6 and 7, each of the intakemanifold outlets 214 aligns and communicates with a respective one ofthe inlet openings 138 in the crankcase cover 118. As shown in FIGS. 4and 6, an intake passage 218 extends between each of the intake manifoldinlets and outlets 206, 214.

The air intake means 170 also includes (FIG. 6) six reed boxes 222supported by the intake manifold 190 in the intake passages 218. Asshown in FIG. 4, each reed box 222 is fixed to the port portion 194 ofthe air intake manifold 190 and (FIGS. 6 and 7) extends rearwardly froma respective intake manifold outlet 214 through a crankcase cover inletopening 138 and into an associated crankcase passage portion 142. Thereed boxes 222 operate conventionally to afford passage of intake airinto the crankcases 130 from the intake manifold 190 and to prevent airflow out of the crankcases 130.

The starboard portion 198 of the intake manifold 190 includes (FIGS. 5,8 and 11) a generally vertically extending wall or web 230. Thestarboard portion 198 also includes (FIGS. 4 and 11) a generally tubularthrottle housing 234 extending rearwardly from the web 230. As bestshown in FIG. 4, the throttle housing 234 is laterally offset (towardstarboard) from the intake manifold mounting surface 134 of thecrankcase cover 118. The throttle housing 234 partially defines athrottle passage 238 extending through the web 230 between a rearwardlyopening inlet end 242 and a forwardly opening outlet end 246 adjacentthe plenum mounting surface 202. A throttle plate 250 (FIGS. 3 and 4) issupported within the throttle passage 238 for pivotal movement about agenerally horizontal axis. The starboard portion 198 of the intakemanifold 190 also includes (FIGS. 8 and 11) an idle air passage 254adjacent the throttle housing 234. The idle air passage 254 extendsthrough the starboard portion web 230 to afford air flow into the engine42 when the throttle passage 238 is closed by the throttle plate 250during engine idling.

As shown in FIG. 2, the intake manifold 190 has an upper surface 258extending laterally across the starboard and port portions 198, 194. Forreasons discussed below, the upper surface 258 has thereon (FIGS. 8 and11) adjacent its most starboard end an alternator mounting boss 262.Located toward port from the alternator mounting boss 262 is a pair ofspaced-apart electronic control unit mounting bosses 266.

The starboard portion 198 of the intake manifold 190 also includes(FIGS. 8 and 11) a lower portion 270 having extending verticallydownwardly therefrom a throttle cable mount 274. For reasons discussedbelow, the throttle cable mount 274 has therethrough a pair of boltholes 278.

The air intake means 170 also includes (FIGS. 2-6 and 9) a plenum cover282 mounted on the intake manifold 190. The plenum cover 282 ispreferably made of plastic and includes (FIG. 9) a rearwardly facingintake manifold mounting surface 286 mating with the plenum mountingsurface 202 of the intake manifold 190. As best shown in FIG. 4, theplenum cover 282 cooperates with the intake manifold 190 to definetherebetween a common intake chamber 290 located forwardly of thestarboard portion 198 of the intake manifold 190. The intake chamber 290extends substantially the entire vertical extent of the plenum cover 282and communicates with the outlet end 246 of the throttle passage 238 andwith the idle air passage 254.

As best shown in FIGS. 6 and 9, the plenum cover 282 also cooperateswith the intake manifold 190 to define six intake runner passages 294located forwardly of the port portion 194 of the intake manifold 190.More particularly, the plenum cover 282 includes six pairs of verticallyspaced-apart, opposed walls 298 that extend generally rearwardly fromthe forward end of the plenum cover 282. Each pair of walls 298 definestherebetween a respective runner passage 294 such that the runnerpassage 294 extends laterally and generally horizontally between theintake chamber 290 and a respective one of the intake manifold inlets206. Preferably, the runner passages 294 are substantially equal inheight and length, and extend uniformly between the intake chamber 290and the intake manifold inlets 206.

As best shown in FIGS. 6 and 14, the uppermost of the walls 298 definesa top wall 302 that extends horizontally and is substantially flush tothe respective upper surfaces of the intake manifold 190 and thecrankcase cover 118. For reasons discussed below, the top wall 302 hastherein (see FIG. 14) an opening 306 communicating with the intakechamber 290 and with the uppermost runner passage 294.

As mentioned above, and as best shown in FIG. 4, the air intake means170, including the plenum cover 282 and intake manifold 190, provides aU-shaped path 174 for providing a flow of intake air to the crankcases130. More particularly, air flowing into the engine 42 flows forwardlythrough the throttle and idle air passages 238, 254, forwardly andthrough the intake chamber 290, rearwardly and through the runnerpassages 294, and rearwardly through the intake passages 218 and thereed boxes 222. Air flowing rearwardly through the reed boxes 222 passesinto the associated crankcase passages 142, and into the crankcases 130.From the crankcases 130, air flows through the transfer passages 90 tothe combustion chambers 106. As shown in FIG. 4, at least one of therunner passages 294 lies in a horizontal plane including the throttlepassage 254 such that the U-shaped path 174 lies in a horizontal plane.Also, each of the runner passages 294 extends horizontally from thecommon intake chamber 290 which is part of the upstream leg 182 of theair flow path 174. Accordingly, each of the runner passages 294 definesa horizontal plane in which portions of the upstream and downstream legs182, 178 lie.

The air intake means 170 can be tuned to optimize the rate of mass airflow to the crankcases 130 for a particular range of engine speeds.Because the runner passages 294 and intake chamber 290 have respectiveconfigurations defined in part by the inner surface of the plenum cover282, which is preferably made of plastic, the configuration of therunner passages 294 and the intake chamber 290 can be readily modifiedto tune the air intake means for various ranges of engine speeds bymodifying a single component of the engine, i.e. by modifying theconfiguration of the plenum cover 282.

The engine 42 also comprises (FIG. 14) an electronic control unit 310mounted on the top wall 302 of the plenum cover 282 and on the uppersurface 258 of the intake manifold 190 in a position overlying andclosing the opening 306 in the top wall 302 of the plenum cover 282. Theelectronic control unit 310 is fastened to the electronic control unitmounting bosses 266 and to a mounting boss 311 (FIG. 14) in the top wall302 of the plenum cover 282. In order to protect the electronic controlunit 310 from heat developed primarily by the electronic control unit310 itself, the engine 42 also includes means 312 for cooling theelectronic control unit 310. While various suitable constructions forthe cooling means 312 can be used, in the illustrated embodiment, thecooling means 312 includes, on the electronic control unit 310, aplurality of cooling fins 313 extending through the opening 306 in thetop wall 302 and into the intake chamber 290 and the uppermost runnerpassage 294. Intake air flowing into the intake chamber 290 passes thecooling fins 313 and acts as a heat sink. For reasons discussed below,the electronic control unit 310 also includes (FIGS. 2 and 3) avertically extending timing pointer mount 314 located adjacent theinterface of the plenum cover 282 and the intake manifold 190. While notshown, the timing pointer mount 314 has therethrough a laterallyextending slot adapted to receive a timing pointer mounting bolt 315(FIG. 3).

The engine 42 also comprises (FIG. 3) means 316 supported by the intakemanifold 190 for controlling air flow to the engine 42 in response tooperator input. While various suitable air flow controlling means 316can be employed, in the illustrated embodiment, such means includes theabove-described throttle plate 250, and a throttle linkage 318 supportedby the intake manifold 190 and operably connected to the throttle plate250. A suitable arrangement for the throttle linkage 318 is described ingreater detail in the above-mentioned U.S. Ser. No. 07/954,492, whichwas filed Sep. 30, 1992, which is assigned to the assignee hereof, andwhich is incorporated herein by reference. A throttle control cable 322for transmitting operator input is operably connected to the throttlelinkage 318 and is supported by a throttle and shift cable mountingassembly 326 fixed by bolts (not shown) extending through the holes 278in the throttle cable mount 274. A suitable throttle and shift cablemounting assembly 326 is described in greater detail in U.S. Pat. No.5,080,618 which issued Jan. 14, 1992 and which is incorporated herein byreference.

The engine 42 further comprises (FIG. 3) a timing pointer 330 fixed bythe timing pointer mounting bolt 315 along the slot in the timingpointer mount 314. The timing pointer 330 is thus indirectly supportedby the plenum cover 282 and by the intake manifold 190. The engine alsocomprises a flywheel 334, and the timing pointer 330 is used inconjunction with markings on the flywheel 334 to determine the sparktiming of the engine 42.

The engine 42 further comprises an alternator 338 (shown in FIG. 3 andin phantom in FIG. 2) mounted on the intake manifold 190 and on thecylinder block 50. The alternator 338 is mounted, in part, on thealternator mounting boss 262 and on a clevis-like fixture 342 (FIG. 3)bolted to the forward end 54 of the cylinder block 50. When so mounted,the alternator 338 extends generally vertically and is located above thethrottle housing 234 and starboard of the crankcase cover 118.

One of the advantages of the engine 42 is that it includes relativelyfew components, thereby simplifying its manufacture and assembly. Theengine 42 is further simplified by the mounting of several enginecomponents both directly and indirectly on a single supportingcomponent, i.e., the intake manifold 190, which also reduces the numberof engine parts that are required.

Another advantage of the engine 42 is that the air intake provides anair intake flow path that, by virtue of its relatively smooth and simpleconfiguration, provides increased efficiency in supplying air to thecrankcases 130. In addition, the air intake of the engine 42 can beeasily tuned for a variety of engine speeds yet can also be sized to fitwithin the envelope dictated by conventional engine cowls.

Another advantage of the engine 42 is the provision of an air-cooledelectronic control unit 312 mounted on the air intake manifold 190. Theprovision of an air-cooled electronic control unit eliminates the needfor a water jacket surrounding and cooling the electronic control unit,and eliminates the need for a coolant line connected to such a waterjacket.

FIGS. 15-17 illustrate an engine 542 that is an alternative embodimentof the invention. The engine 542 is identical in construction to theengine 42 except for the below described differences. Accordingly,common reference numerals are used to identify features that are commonto the engines 42 and 542.

The engine 542 includes a cylinder block 50 and a crankcase cover 118fixed to the cylinder block 50. The cylinder block 50 and the crankcasecover 118 define therebetween a plurality of crankcases and support acrankshaft (the crankcases and crankshaft are not shown in FIGS. 15-17).The engine 542 also includes an intake manifold 590 that is mounted onthe forward end of the crankcase cover 118. The intake manifold 590includes integrally cast port and starboard portions 594, 598 and (seeFIG. 17) a plurality of intake manifold inlets 606 located in the portportion 594.

The engine 542 also includes (see FIGS. 15 and 16) a plenum cover 682mounted on the forward end of the intake manifold 590. The plenum cover682 is made of plastic and provides an inner surface that cooperateswith the intake manifold 590 to define therebetween a common intakechamber (not shown) located forwardly of the intake manifold 590 and aplurality of intake runner passages 694 that each extend from the commonintake chamber and a respective one of the intake manifold inlets 606.As best shown in FIGS. 15 and 16, and unlike the top wall 302 of theplenum cover 282, the uppermost or top wall 702 of the plenum cover 682provides an imperforate surface, i.e. the wall 702 does not have thereinany openings or other means providing access to the interior of theplenum cover 682.

The engine 542 also includes (FIGS. 15 and 17) an electronic controlunit 710 mounted on the port portion 594 of the intake manifold 590.More particularly, and as best shown in FIG. 17, the port portion 594 ofthe intake manifold 590 includes a mounting boss 714 that faceslaterally outwardly. The electronic control unit 710 includes (see FIG.15) a base 718 that is fixed to the mounting boss 714 by a bolt 722. Thebase 718 provides means 726 for cooling the electronic control unit 710.While various suitable cooling means 726 could be employed, in theillustrated embodiment, the cooling means 726 includes a water jacket730 (shown schematically in FIG. 15) located within the base 718. Thecooling means 726 also includes a pair of water hoses 734 (only oneshown in FIG. 15) that are connected to a suitable source of coolant(not shown), such as a water jacket in the cylinder block, and thatprovide a flow of coolant to and from the water jacket 730.

The engine 542 also includes (See FIG. 16) a timing pointer 750 that ismounted directly on the intake manifold 590. In particular, and asillustrated in FIG. 16, the intake manifold 590 provides a timingpointer mount 758 extending upwardly from the upper portion of theintake manifold 590. The timing pointer 750 is fixed to the timingpointer mount 758 by suitable means such as a bolt 762.

Like the engine 42, the engine 542 also includes an alternator 638, athrottle linkage 318 and a throttle and shift cable mounting assembly326, each of which is mounted on the intake manifold 590. While theengines 42 and 542 include respective intake manifolds 190 and 590respectively supporting various specifically disclosed enginecomponents, it should be readily understood that the intake manifolds190 and 590 can be readily modified support additional various enginecomponents. For example, the intake manifolds. 190 and 590 can bereadily modified by providing appropriately located mounting bosses in avariety of positions, including on the lower portions of the intakemanifolds 190 and 590, to provide support for fuel pumps and fuel flowregulators.

Various features of the invention are set forth in the following claims.

We claim:
 1. A two-stroke internal combustion engine comprising acylinder block including a generally planar crankcase mounting surfacehaving therein a crankcase recess, a crankcase cover including agenerally planar cylinder block mounting surface mating with saidcrankcase mounting surface and having therein a crankcase recess alignedwith said crankcase recess in said cylinder block and defining therewitha crankcase, and air intake means for supplying a flow of air to saidcrankcase, said air intake means defining a U-shaped.Iadd., generallyhorizontal, .Iaddend.air intake path having a downstream leg directedtoward and generally perpendicular to said crankcase mounting surface.Iadd.and affording air flow in the rearward direction toward saidcrankcase .Iaddend.and having an upstream leg .Iadd.extending.Iaddend.generally parallel to and directed opposite said downstream leg.Iadd.and affording air flow in the forward direction.Iaddend..
 2. Anengine as set forth in claim 1 wherein said intake path has a pluralityof downstream legs. .[.3. An engine as set forth in claim 1 wherein saidupstream and downstream legs define a generally horizontal plane..].4.An engine as set forth in claim 1 wherein said crankcase mountingsurface and said cylinder block mounting surface lie in a generallyvertically extending plane.
 5. An engine as set forth in claim 1 whereinsaid crankcase cover includes an intake manifold mounting surface havingtherein an inlet opening communicating with said crankcase.
 6. An engineas set forth in claim 5 wherein said air intake means includes an intakemanifold including a crankcase cover mounting surface mating with saidintake manifold mounting surface.
 7. An engine as set forth in claim 6wherein said intake manifold includes a plenum mounting surface opposedto said crankcase cover mounting surface and an intake passage extendingfrom said plenum mounting surface to said crankcase cover mountingsurface and communicating with said inlet opening.
 8. An engine as setforth in claim 7 wherein said intake manifold includes a throttlepassage extending from said plenum mounting surface parallel to saidintake passage, said throttle passage being laterally offset from saidintake manifold mounting surface.
 9. An engine as set forth in claim 8wherein said intake means further includes a plenum cover including aninner surface mating with said plenum mounting surface, said plenumcover cooperating with said intake manifold to define an intake chambercommunicating with said throttle passage.
 10. An engine as set forth inclaim 9 wherein said plenum cover also cooperates with said intakemanifold to define an intake runner passage communicating between saidintake chamber and said intake passage.
 11. A two-stroke internalcombustion engine comprising an engine block defining a crankcaseincluding an intake manifold mounting surface having therein an inletopening communicating with said crankcase, an intake manifold having acrankcase cover mounting surface mating with said intake manifoldmounting surface, a plenum mounting surface spaced from and extending inparallel relation to said crankcase cover mounting surface, and anintake passage extending from said plenum mounting surface to said inletopening and generally perpendicularly to said plenum mounting surface,and a plenum cover including an inner surface mating with said plenummounting surface, and an intake runner passage communicating with saidintake passage and extending from said intake passage in lateralrelation to said plenum mounting surface.
 12. An engine as set forth inclaim 11 wherein said plenum cover also cooperates with said intakemanifold to define an intake chamber, and wherein said intake runnerpassage communicates between said intake chamber and said intakepassage.
 13. An engine as set forth in claim 11 wherein said engineblock means includes a cylinder block including a crankcase mountingsurface having therein a crankcase recess, and a crankcase coverincluding a cylinder block mounting surface mating with said crankcasemounting surface and having therein a crankcase recess aligned with saidcrankcase recess in said cylinder block to define said crankcase, andwherein said crankcase cover includes said intake manifold mountingsurface.
 14. An engine as set forth in claim 11 wherein said engineblock means defines a plurality of crankcases, wherein said intakemanifold mounting surface has therein a plurality of inlet openings eachof which respectively communicates with a respective crankcase, andwherein said plenum cover and said intake manifold cooperate to define aplurality of intake runner passages each of which respectivelycommunicates with a respective inlet opening.
 15. An engine as set forthin claim 14 wherein said engine block means includes a V-type cylinderblock, and wherein all of said inlet openings are in-line.
 16. Atwo-stroke internal combustion engine comprising a cylinder blockincluding a generally planar crankcase cover mounting surface havingtherein a crankcase recess, a crankcase cover including a generallyplanar cylinder block mounting surface mating with said crankcase covermounting surface and having therein a crankcase recess aligned with saidcrankcase recess in said cylinder block to define a crankcase, airintake means for supplying air to said crankcase and including athrottle housing and a wall located intermediate said throttle housingand said crankcase and partially defining an air passagewaycommunicating between said throttle housing and said crankcase, saidwall having therein an opening communicating with said passageway, anelectronic control unit mounted on said wall, and means for cooling saidelectronic control unit including a plurality of cooling fins extendingfrom said electronic control unit and through said opening and into saidpassageway.
 17. A two-stroke internal combustion engine comprising anengine block means defining a crankcase and including an intake manifoldmounting surface having therein an inlet opening communicating with saidcrankcase, an intake manifold including a crankcase cover mountingsurface mating with said intake manifold mounting surface, a plenummounting surface opposed to said crankcase cover mounting surface, anintake passage extending from said plenum mounting surface to saidcrankcase cover mounting surface and communicating with said inletopening, and a throttle passage extending from said plenum mountingsurface and parallel to said intake passage, said throttle passage beinglaterally offset from said intake manifold mounting surface, and meansfor conducting air from said throttle passage to said intake passage.18. An engine as set forth in claim 17 wherein said intake manifoldsupports at least one of any of an electronic control unit, a pluralityof reed boxes, a throttle linkage which is connected to a throttleplate, a cable mount which supports a throttle control cable, a timingpointer, and an alternator.
 19. An outboard motor having forward andrearward ends and comprising a propulsion unit adapted to be mounted onthe transom of a boat, said propulsion unit including a propeller shaftwith a rearward end adapted to have mounted thereon a propeller, andsaid propulsion unit also including a two-stroke internal combustionengine drivingly connected to said propeller shaft, said engineincluding engine block means defining a crankcase and air intake meansfor supplying air to said crankcase, said air intake means defining aU-shaped.Iadd., generally horizontal, .Iaddend.air intake path having arearwardly directed downstream leg .Iadd.affording air flow in therearward direction toward said crankcase .Iaddend.and having a forwardlydirected upstream leg .Iadd.extending .Iaddend.generally parallel tosaid downstream leg .Iadd.and affording air flow in the forwarddirection.Iaddend..
 20. A two-stroke internal combustion enginecomprising an engine block including a cylinder block including acrankcase cover mounting surface having therein a crankcase recess, anda crankcase cover including a cylinder block mounting surface matingwith said crankcase cover mounting surface and having therein acrankcase recess aligned with said crankcase recess in said cylinderblock to define a plurality of crankcases, said crankcase cover alsoincluding an intake manifold mounting surface having therein a likeplurality of inlet openings respectively communicating with saidcrankcases, a throttle housing defining a throttle passage and includinga plenum mounting surface, a throttle valve in said throttle passage, anintake manifold including a crankcase cover mounting surface mating withsaid intake manifold mounting surface, a plenum mounting surface opposedto said crankcase cover mounting surface, and a like plurality of inletpassages respectively communicating between said plenum mounting surfaceand said inlet openings of said crankcase cover, and a plenum memberwhich is mounted on said plenum mounting surfaces of said throttlehousing and said intake manifold, which is separable from both saidintake manifold and said throttle housing and which defines a likeplurality of intake passages having respective outlet ends communicatingrespectively with said inlet passages of said intake manifold and havingrespective inlet ends communicating with said throttle passage such thatthe intake of said engine can be tuned solely by modifying theconfiguration of said plenum member.